Nanotechnology is concerned with the fabrication and application of materials, structures, devices, and systems at the atomic and molecular level. Nanotechnology typically is concerned with structures and devices having elements or features that are less than about 100 nanometers in size. At these dimensions, such structures and devices often exhibit novel and significantly improved physical, chemical, and biological properties, phenomena, and processes due to their extremely small size. The behavior of such structures and devices may not be predictable based on the behavior exhibited by larger, but otherwise identical structures and devices. Nanotechnology is currently making significant contributions to the fields of computer storage, semiconductors, biotechnology, manufacturing and energy.
Nanowires are fundamental structures that are often used in nanoscale structures and devices. Nanowires are wire-like structures that typically have diameters of less than about 100 nanometers. In addition to functioning as conventional wires for interconnection applications, nanowires have a wide variety of other potential applications. Recently, devices and systems such as field-effect transistors, radiation detectors, light emitting diodes, lasers, and sensors have been described that employ nanowires in their design.
Many nanowires described in the art include conventional semiconductor materials such as silicon-based materials and germanium-based materials.
One method of forming such nanowires is the vapor-liquid-solid (VLS) chemical synthesis process. Generally, this method involves depositing particles of a catalyst material such as gold or titanium on a surface of a structure on which it is desired to grow nanowires. The structure is provided within a chamber and heated to temperatures typically ranging between about 500° C. and about 1000° C. Precursor gasses that include elements that will be used to form the nanowires are introduced into the chamber. The particles of catalyst material cause the precursor gasses to at least partially decompose into their respective elements, some of which are transported on or through the particles of catalyst material and deposited on the underlying surface. As this process continues, a nanowire is formed or grown with the catalyst particle remaining on the growing tip or end of the nanowire.
Nanowires that include a heterogeneous structure have also been described in the art. For example, longitudinal heterostructure nanowires (LOHN) have been described in which the composition of the nanowire varies along the longitudinal length thereof. Similarly, coaxial heterostructure nanowires (COHN) have been described in which the composition of the nanowire varies in the radial direction. Nanowires that include such heterogeneous structures have been described that include multiple regions of doped semiconductor materials that form pn, pnp, and npn junctions.
Many areas of technology, such as optical signal processing for example, employ light-emitting diodes (LED's) and laser devices such as vertical cavity surface emitting lasers (VCSEL's) that include active or gain material disposed within a resonant cavity. The resonant cavity may be used to ensure that the spectral line width of the light emitted by the active material is narrow and to provide emitted light having high directivity. Quantum dots that are formed from active material have been provided within resonant cavities to provide such light-emitting diodes and laser devices. One challenge to optimizing the performance of such devices, however, has been the inability to precisely control the position of such quantum dots within the resonant cavity. Therefore, there is a need in the art for methods of precisely positioning quantum dots within resonant cavities.